The use of FinFETs is very attractive for manufacturing for increasing the density and electrical characteristics of MOS transistors. The fin rises above a substrate to function as the channel so that a major portion of the transistor is vertical and not lateral. The channel direction is lateral or horizontal but is in a structure that is above the surface of the substrate. One of the difficulties however, has been the manufacture of these vertical structures over silicon on insulator (SOI) during the process of thinning the silicon fin by oxidation and cleans. Oxidizing and consuming a portion of the fin is desired in order to form sub-lithographic fin dimensions by cleaning the oxide.
However, the oxide region under the fin gets etched and creates a void. This void leads to undesirable manufacturing problems such as the fins physically falling over or collapsing and allowing for future process layers such as the gate electrode to be difficult to remove from the voids.
Where FinFETs are formed on a bulk silicon substrate, the oxidization of wide structural elements, such as the source and drain, will result in unoxidized portions of silicon underlying elements such as a source or drain that are connected to other unoxidized portions of silicon through the silicon bulk. This requires extensive isolation techniques to electrically isolate adjacent transistors. The failure to oxidize the portions of silicon in a bulk silicon substrate underlying these elements is from the fact that an oxidation which would be sufficient to prevent the problem would result in oxidizing the channel region of the fin. The oxidization of the channel region makes the channel region electrically inactive and results in failure of the FinFET.
Skilled artisans appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve the understanding of the embodiments of the present invention.